Camera having display device utilizing TFT

ABSTRACT

A camera includes a display device which has thin film transistors (TFT). A gate insulating film of the TFT has a first insulating film including silicon oxide and a second insulating film including silicon nitride. A third insulating film including silicon nitride is formed over the first and second insulating films and a gate electrode. The third insulating film is in direct contact with an upper surface of an extending portion of the first insulating film and an upper surface of an extending portion of the second insulating film.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 10/657,137, filed on Sep. 9, 2003, which is a divisional applicationof U.S. application Ser. No. 09/967,697, filed on Sep. 28, 2001, nowU.S. Pat. No. 6,657,228, which is a continuation of U.S. applicationSer. No. 08/862,895, filed on May 23, 1997, now U.S. Pat. No. 6,316,787,which claims the benefit of a foreign priority application filed inJapan as Ser. No. 8-165272, on Jun. 4, 1996, all of which areincorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor integrated circuithaving a plurality of thin film transistors (TFT) and more particularlyto a monolithic active matrix circuit having an active matrix circuitand a logic circuit (called also as a peripheral circuit) for driving iton one and the same substrate and to a fabrication method thereof. Thesemiconductor integrated circuit fabricated by the present invention maybe formed either on an insulating substrate such as glass and on aninsulating coating film formed on a semiconductor substrate such asmonocrystal silicon for example. The present invention exhibits itseffect specifically in a semiconductor integrated circuit having a largematrix which operates at low speed and a logic circuit for driving itwhich is required to operate at high speed, such as a liquid crystaldisplay.

DESCRIPTION OF RELATED ART

Recently, researches on an insulated gate type semiconductor devicehaving a thin film semiconductor layer (also called as an active layer)on an insulating substrate are being conducted and specifically,researches on a thin film insulated gate transistor, i.e. a so-calledthin film transistor (TFT), are being actively conducted. They arecategorized as an amorphous silicon TFT or a crystal silicon TFTdepending on a material and a crystal state of the semiconductor to beused.

Generally, a semiconductor in the amorphous state has a small fieldmobility, so it cannot be utilized for a TFT which is required tooperate at high speed. Then, research and development on the crystalsilicon TFT are being conducted in order to fabricate a higherperformance circuit in these days.

In those TFTs, a thin film semiconductor region of each individual thinfilm transistor is isolated and hence, the channel portion has not beengrounded like the conventional semiconductor integrated circuit on asemiconductor chip. Due to that, deterioration or failure peculiar tothe TFT have occurred sometimes. For instance, with regard to a hotcarrier implantation phenomenon, it has been extremely difficult toremove accumulated charge because the channel has been put in the stateof floating potential.

Then, a gate insulating film has been thickened or applied voltage hasbeen reduced in order to prevent the deterioration and the like causedby the implantation of carrier. However, operating speed decreases ifthe gate insulating film is thickened. It has been also difficult toreduce the applied voltage because of the requirement of a device.Because driving voltage of a matrix circuit is determined depending on aliquid crystal material in the monolithic active matrix circuit used fora liquid crystal display in particular, it is difficult to change itarbitrarily.

However, the operating speed of the logic circuit decreases if the gateinsulating film is thickened. Then, driving voltage has to be increasedto maintain the operating speed, increasing power consumption.

FIG. 11A is a block diagram showing the monolithic active matrix circuitused for a liquid crystal display. In the figure, a column driver 1 anda row driver 2 are provided on a substrate 7 as peripheral drivercircuits, pixel circuits (pixels) 4 each comprising a transistor and acapacitor are formed in a matrix area 3 and the matrix area is connectedwith the peripheral circuits through wires 5 and 6.

Among the TFTs used for the driver circuits, high operating speed isrequired to the TFT composing the logic circuit such as a shift registerand high withstand voltage is required to the TFT used in the pixelcircuit. Even in the driver circuits, a part of transistors in aswitching circuit (e.g. buffer circuit) is required to have highwithstand voltage, rather than high operating speed.

Because the high operating speed and the high withstand voltage arecontradictory requirements as described above, it has been difficult toform those transistors on one and the same substrate in one and the sameprocess especially when it is required to reduce the power consumption.Accordingly, it is an object of the present invention to solve suchdifficult problems.

SUMMARY OF THE INVENTION

The present invention is characterized in that a thickness of a gateinsulating film in a circuit in which priority is given to highoperating speed is changed from that of a gate insulating film in acircuit in which priority is given to high withstand voltage. That is,the former is made to be a circuit which is driven in low voltage andoperates at high speed and the latter is made to be a circuit havinghigh withstand voltage by reducing the thickness of the gate insulatingfilm of the former as compared to that of the latter.

In this case, among peripheral circuits, the circuits in which priorityis given to high operating speed include logic circuits such as a shiftregister, a CPU, a memory circuit and a decoder circuit. Further, amongperipheral circuits, the circuits in which priority is given to highwithstand voltage include a high withstand voltage switching circuit, abuffer circuit and others.

A matrix circuit is also the circuit in which priority is given to highwithstand voltage, though it is not the peripheral circuit.

Their difference is distinguished by a variation of voltage applied tothe gate electrode in general. That is, the width of variation ofvoltage applied to the gate electrode is small in the former rather thanin the latter.

Then, a semiconductor integrated circuit of a first invention ischaracterized in that a thickness of at least one gate insulating filmof the thin film transistor of the circuit in which priority is given tohigh operating speed is 80% or less of a thickness of a gate insulatingfilm of the thin film transistor of the circuit in which priority isgiven to high withstand voltage.

A semiconductor integrated circuit of a second invention ischaracterized in that at least one layer of another insulating layer isused for at least one gate insulating film of the thin film transistorof the circuit in which priority is given to high withstand voltage inaddition to an insulating layer composing at least one gate insulatingfilm of the thin film transistor of the circuit in which priority isgiven to high operating speed.

A semiconductor integrated circuit of a third invention is characterizedin that when at least one gate insulating film of the thin filmtransistor of the circuit in which priority is given to high operatingspeed is assumed to be a first insulating layer, at least one gateinsulating film of the thin film transistor of the circuit in whichpriority is given to high withstand voltage is composed of, in additionto the first insulating layer, a second insulating layer formed in adifferent process from the first insulating layer.

A semiconductor integrated circuit of a fourth invention ischaracterized in that in the semiconductor integrated circuit having afirst thin film transistor and a second thin film transistor each havinga gate insulating film whose thickness is different, the thickness ofthe gate insulating film of the first thin film transistor is 80% orless of the thickness of the gate insulating film of the second thinfilm transistor and a length of a channel of the first thin filmtransistor is 80% or less of a length of a channel of the second thinfilm transistor.

The semiconductor integrated circuit of the fourth invention is alsocharacterized in that the thin film transistor used in the peripheralcircuit which is required to operate at high speed is micronized inaccordance to scaling law.

Specifically, the present invention is characterized in that the lengthof the channel in the circuit in which priority is given to highoperating speed is changed from that of the channel in the circuit inwhich priority is given to high withstand voltage. That is, the lengthof the channel of the former is shortened as compared to that of thelatter, or the length of the channel of the latter is prolonged ascompared to that of the former, so as to make the former a transistorwhich is driven in low voltage and which operates at high speed and thelatter a transistor of high withstand voltage.

Here, the scaling law to reduce physical dimensions of the TFT or wiringcomposing it, an interlayer film and others in inversely proportional toa certain coefficient. It allows enhancement of performance to beachieved in the same time with highly densified separation of devices.

According to the present invention, electrical characteristics of theperipheral circuit which is required to operate at high speed isimproved by micronizing the channel length and the thickness of the gateinsulating film in particular.

The micronization of the channel length may be achieved by modifying ashape of a mask in forming the gate electrode.

In the first through fourth invention described above, it is possible toinclude a low concentration impurity region that is formed by utilizinga difference of the thickness of the gate insulating films in the thinfilm transistor of the circuit in which priority is given to highwithstand voltage. It allows high withstand voltage characteristics tobe enhanced further.

Further, in the third invention described above, the chemicalcomposition of the first insulating layer may be differentiated fromthat of the second insulating layer. Thereby, it becomes advantageous infabricating them.

Similarly to that, in the third invention described above, only eitherone of the first insulating layer or the second insulating layer may beformed by means of thermal oxidation. It is of course possible to formthe both by means of the thermal oxidation.

As for a method for fabricating the inventive semiconductor integratedcircuit, there are the following inventions. The fifth inventioncomprises steps of:

1) forming a thin film semiconductor region utilized for a thin filmtransistor of a circuit in which priority is given to high withstandvoltage and a thin film semiconductor region utilized for a thin filmtransistor of a circuit in which priority is given to high operatingspeed;

2) forming a first insulating layer covering both of the thin filmsemiconductor regions;

3) selectively removing the first insulating layer to remove all thefirst insulating layer covering the thin film semiconductor regioncomposing at least one of the thin film transistor of the circuit inwhich priority is given to high operating speed by; and

4) forming a second insulating layer covering both of the thin filmsemiconductor regions.

The sixth invention comprises steps of:

1) forming a thin film semiconductor region utilized for a thin filmtransistor of a circuit in which priority is given to high withstandvoltage and a thin film semiconductor region utilized for a thin filmtransistor of a circuit in which priority is given to high operatingspeed;

2) forming a first insulating layer covering both of the thin filmsemiconductor regions;

3) forming a second insulating layer covering the first insulatinglayer; and

4) selectively removing the second insulating layer to remove all thefirst insulating layer covering the thin film semiconductor regioncomposing at least one of the thin film transistor of the circuit inwhich priority is given to high operating speed.

The seventh invention comprises steps of:

1) forming a thin film semiconductor region utilized for a thin filmtransistor of a circuit in which priority is given to high withstandvoltage and a thin film semiconductor region utilized for a thin filmtransistor of a circuit in which priority is given to high operatingspeed;

2) selectively forming a first insulating layer covering both of thethin film semiconductor region except part of the thin filmsemiconductor region composing at least one of the thin film transistorsof at least the circuit in which priority is given to high operatingspeed; and

3) forming a second insulating layer covering both of the thin filmsemiconductor regions.

In the fifth through seventh inventions described above, the firstinsulating layer may be formed by means of thermal oxidation. The secondinsulating layer may be also formed by means of thermal oxidation as amatter of course.

The fifth through seventh inventions described above may furthercomprise a step of forming gate electrodes whose width is differentowing to shapes of mask of the gate electrodes so that the width of thegate electrode of the second thin film transistor is larger than thewidth of the gate electrode of the first thin film transistor.

It also comprises a step of forming a channel region having almost thesame width with the width of the gate electrode under the gate electrodein a step of doping to the active layer.

While the length of the channel of the first thin film transistor hasbeen set to be 80% or less of the length of the channel of the secondthin film transistor, it has been found that the electricalcharacteristics such as operating speed improves when the ratio of thelength of the channel of the first thin film transistor to that of thesecond thin film transistor is set preferably at 0.1 to 0.5.

Therefore, the ratio of the width of the gate electrode of the firstthin film transistor to the width of the gate electrode of the secondthin film transistor has been set within a range of 0.1 to 0.5.

The electrical characteristics such as operating speed improves furtherwhen the thickness of the gate insulating film of the first thin filmtransistor and the second thin film transistor is adjusted in accordanceto this ratio.

Thereby, the thickness of the gate insulating film or the channel lengthmay be changed in the circuit which is required to operate at high speed(e.g. a logic circuit in a monolithic active matrix circuit) and thecircuit which is required to have high withstand voltage (a matrixcircuit in the monolithic active matrix circuit). As a result, as forthe monolithic active matrix circuit, the logic circuit which is drivenin low voltage and operates at high speed and the high withstand voltagematrix circuit may be obtained on one and the same substrate, which isthe purpose of the present invention. It is noted that as disclosed in,for example, Japanese Patent Laid Open No. Hei. 7-135323, the disclosureof which is herein incorporated by reference, the present invention isapplicable to a semiconductor integrated circuit in which variousmemories and arithmetic devices are provided as logic circuits on oneand the same substrate (see FIG. 11B). In FIG. 11B, a correction memory8, a memory 9, an input port 10, a CPU 11, and an XY branch 12 areformed on a substrate 7 as well as a column decoder/driver 1, a rowdecoder/driver 2, and an active matrix 3. The present invention will beexplained below in detail with reference to preferred embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A through 1F are section views showing a fabrication processaccording to a first embodiment:

FIGS. 2A through 2F are section views showing a fabrication processaccording to a second embodiment:

FIGS. 3A through 3F are section views showing a fabrication processaccording to a third embodiment:

FIGS. 4A through 4F are section views showing a fabrication processaccording to a fourth embodiment:

FIGS. 5A through 5F are section views showing a fabrication processaccording to a fifth embodiment:

FIGS. 6A through 6F are section views showing a fabrication processaccording to a sixth embodiment:

FIGS. 7A through 7C are section views showing a fabrication processaccording to an eighth embodiment:

FIGS. 8A through 8C are section views showing a fabrication processaccording to a ninth embodiment:

FIGS. 9A through 9C are section views of the fabrication process of thefifth embodiment using a resist film to selectively obtain a thermaloxide film;

FIGS. 10A through 10C are section views of the fabrication process ofthe sixth embodiment using a resist film to selectively obtain a thermaloxide film;

FIGS. 11A and 11B show structural examples of a monolithic active matrixcircuit; and

FIGS. 12A through 12D show examples of equipment using a flat paneldisplay according to a tenth embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

[First Embodiment]

FIGS. 1A through 1F are section views showing a fabrication processaccording to the present embodiment. In FIGS. 1A through 1F, a logiccircuit 101 is formed on the left side of the paper and a matrix circuit102 on the right side. At first, a base film (not shown) of siliconoxide of 2000 Å in thickness is formed on a substrate (Corning 7059) 11by means of sputtering. Further, an intrinsic (I-type) amorphous siliconfilm of 500 to 1500 Å in thickness, or 500 Å for example, is depositedby means of plasma CVD. Then, it is crystallized by means of knownthermal annealing. It may be crystallized by a method of irradiatinglight energy beam such as laser light or a lamp, instead of the thermalannealing, or by using combinations of the methods. The method ofirradiating with a lamp is called a rapid thermal annealing (RTA)method.

The silicon film thus obtained is patterned by means of photolithographyto separate into islands to form island regions 12 a and 12 b for TFTsof a logic circuit and an island region 12 c for a TFT of a matrixcircuit.

Further, a silicon oxide film 13 of 1000 Å in thickness is deposited asa first gate insulating layer by means of sputtering. In the sputtering,silicon oxide is used as a target, a substrate temperature during thesputtering is 200 to 400° C., or 350° C. for example, and sputteringatmosphere composed of oxygen and argon is set to have a ratio ofargon/oxygen=0 to 0.5, or 0.1 or less for example (FIG. 1A).

Further, a silicon nitride film of 1500 to 3000 Å in thickness isdeposited by means of plasma CVD. It is then etched except a portionnear a channel of the TFT of the matrix circuit to obtain a second gateinsulating layer 14 (FIG. 1B).

Following to that, a silicon film (containing 0.1 to 2% of phosphorus)of 3000 to 8000 Å in thickness, or 6000 Å for example, is deposited bymeans of low pressure CVD. Then, it is etched to form gate electrodes 15a, 15 b and 15 c (FIG. 1C).

The first gate insulating layer and the second gate insulating layer arethen etched by using the respective gate electrodes as a mask to exposethe surface of the island-like semiconductor regions. As a result, gateinsulating films comprising the first gate insulating layers 13 a and 13b (both used for the logic circuit) and a gate insulating filmcomprising the first gate insulating layer 13 c and the second gateinsulating layer 14 c (used for the matrix circuit) are obtained (FIG.1D).

Next, impurities (phosphorus and boron) are implanted to the siliconregion by using the gate electrodes as a mask by means of known iondoping. Phosphine (PH₃) and diborane (B₂H₆) are used as the doping gasand the dosage thereof is 1×10¹⁵ to 8×10¹⁵ cm⁻², e.g. 2×10¹⁵ cm⁻² ofphosphorus and 5×10¹⁵ cm⁻² of boron. As a result, a P-type impurityregion 16 a and N-type impurity regions 16 b and 16 c are formed.

After that, the impurities are activated by means of laser annealing.Although a KrF excimer laser (wavelength: 248 nm, pulse width: 20 nsec)is used as the laser, other lasers such as a XeF excimer laser(wavelength: 353 mm), a XeCl excimer laser (wavelength: 308 nm), an ArFexcimer laser (wavelength: 193 nm) and the like may be used. Energydensity of the laser is 200 to 400 mJ/cm², or 250 mJ/cm² for example,and the laser is irradiated by 2 to 10 shots, or 2 shots for example,per one spot. The substrate is heated up to 100 to 450° C., or 250° C.for example, in irradiating the laser. Further, this activation can bealso performed by the RTA method.

Thus the impurity regions 16 a through 16 c are activated. This step maybe carried out also by means of thermal annealing (FIG. 1E). Further,this activation can be also performed by the RTA method.

Following to that, a silicon oxide film 17 of 6000 Å in thickness isformed as an interlayer insulator by means of plasma CVD. Contact holesare formed therethrough and electrode/wires 18 a and 18 b for the logiccircuit and an electrode/wire 18 c for the matrix circuit are formed byusing metallic materials such as a multi-layered film of titaniumnitride and aluminum.

Further, an indium tin oxide film (ITO) of 500 to 1000 Å in thickness,or 800 Å for example, is formed by means of sputtering and is patternedto form a pixel electrode 19.

Finally, annealing is implemented at 350° C. for 30 minutes within oneatmospheric pressure of hydrogen atmosphere. Through the above-mentionedsteps, a semiconductor integrated circuit having a P-channel type TFT 20a and an N-channel type TFT 20 b of the logic circuit and a TFT 20 c ofthe matrix circuit is completed. It is noted that a buffer transistor ofa driver circuit may be fabricated in the same manner with thetransistor of the matrix circuit described in the above-mentionedembodiment (FIG. 1F).

[Second Embodiment]

FIGS. 2A through 2F are section views showing a fabrication processaccording to the present embodiment. In FIGS. 2A through 2F, a logiccircuit 201 is formed on the left side of the paper and a matrix circuit202 on the right side. At first, a base film (not shown) of siliconoxide of 2000 Å in thickness is formed on a substrate (Corning 7059) 21.Further, an intrinsic (I-type) crystalline silicon film of 500 to 1500 Åin thickness, or 500 Å for example, is deposited by means of plasma CVD.The silicon film is then separated into islands to form island regions22 a and 22 b for TFTs of a logic circuit and an island region 22 c fora TFT of a matrix circuit.

Further, a silicon oxide film 23 of 1000 Å in thickness is deposited asa first gate insulating layer by means of plasma CVD (FIG. 2A).

Further, a silicon nitride film of 1000 Å in thickness is deposited bymeans of plasma CVD. Then, the silicon nitride film is etched except aportion near a channel of the TFT of the matrix circuit. Here, theportion having a width of 5 μm from an edge of a gate electrode to beformed later is left. Thus, a second gate insulating layer 24 isobtained (FIG. 2B).

Following to that, a silicon film (containing 0.1 to 2% of phosphorus)of 3000 to 8000 Å in thickness, or 6000 Å for example, is deposited bymeans of low pressure CVD. It is then etched to form gate electrodes 25a, 25 b and 25 c (FIG. 2C).

Next, impurities (phosphorus and boron) are implanted to the siliconregion by using the gate electrodes as a mask by means of known iondoping. Phosphine (PH₃) and diborane (B₂H₆) are used as the doping gas.Because through doping, i.e. doping carried out transmitting through agate insulating film, is implemented in the present embodiment,acceleration voltage is increased more than that of the firstembodiment.

Further, while the doping is implemented at higher acceleration voltageat the portion below the gate insulating layer 24 because the gateinsulating film is thick there as compared to other parts, the dosage islowered by 1 to 2 digits.

As a result, an N-type low concentration impurity region 26 d is formedin addition to a P-type high concentration impurity region 26 a andN-type high concentration impurity regions 26 b and 26 c. The technologyfor changing the concentration of impurity by utilizing a difference ofthickness of gate insulating films has been disclosed in such asJapanese Patent Laid Open Nos. Hei. 7-169974, Hei. 7-169975, Hei.7-218932, the disclosures of which are herein incorporated by reference(FIG. 2D).

After activating the impurities, a silicon nitride film 27 of 4000 Å inthickness is formed as a first interlayer insulator by means of plasmaCVD. Contact holes are formed therethrough and electrode/wires 28 a and28 b for the logic circuit and an electrode/wire 28 c for the matrixcircuit are formed by using aluminum (FIG. 2E).

Further, an organic resin film 29 is formed as a second interlayerinsulator. Then, after forming contact holes thereon, an indium tinoxide film (ITO) of 800 Å in thickness is formed by means of sputteringand is patterned to form a pixel electrode 30.

Through the above-mentioned steps, a semiconductor integrated circuithaving a P-channel type TFT 31 a and an N-channel type TFT 31 b of thelogic circuit and a TFT 31 c of the matrix circuit is completed (FIG.2F).

[Third Embodiment]

FIGS. 3A through 3F are section views showing a fabrication processaccording to the present embodiment. In FIGS. 3A through 3F, a logiccircuit 301 is formed on the left side of the paper and a matrix circuit302 on the right side. At first, an intrinsic (I-type) crystallinesilicon film of 800 Å in thickness is formed on a substrate (quartz) 32.The silicon film is then separated into islands to form island regions33 a and 33 b for TFTs of a logic circuit and an island region 33 c fora TFT of a matrix circuit.

Further, a silicon oxide film 34 of 1000 Å in thickness is deposited onthe whole surface by means of plasma CVD (FIG. 3A).

Next, the silicon oxide film 34 at the part of the logic circuit isetched to form a first gate insulating layer 34 a in the matrix circuitregion (FIG. 3B).

Following to that, a gate insulating film of silicon oxide is formed onthe surface of the silicon region by implementing thermal oxidation in850 to 1150° C., or at 950° C. for example. At this time, the siliconoxide is formed so as to be 500 Å in thickness in the logic circuitregion thermally oxidized in the state in which the silicon layer hasbeen exposed. Because the surface of the matrix circuit is covered bythe silicon oxide film formed by means of the plasma CVD, the progressof the thermal oxidation is more moderate and a thickness of the wholesilicon oxide is 1500 Å or less. Thus, gate insulating films 35 a, 35 band 35 c are obtained (FIG. 3C).

Following to that, an aluminum film of 4000 to 6000 Å, or 5000 Å inthickness for example, is deposited by means of sputtering. It is thenetched to form gate electrodes 36 a, 36 b and 36 c. Further, the gateinsulating films 35 a through 35 c are etched by using the gateelectrodes as a mask (FIG. 3D).

Next, impurities (phosphorus and boron) are implanted to the siliconregion by using the gate electrodes as a mask by means of known iondoping to form a P-type impurity region 37 a and N-type impurity regions37 b and 37 c (FIG. 3E).

After activating the impurities, a silicon oxide film 38 of 4000 Å inthickness is formed as an interlayer insulator. Contact holes are formedtherethrough and electrode/wires 39 a and 39 b for the logic circuit andan electrode/wire 39 c for the matrix circuit are formed by aluminum.

Through the above-mentioned steps, a semiconductor integrated circuithaving a P-channel type TFT 40 a and an N-channel type TFT 40 b of thelogic circuit and a TFT 40 c of the matrix circuit is completed (FIG.3F).

The pixel electrode may be added in the manner as described in thesecond embodiment.

[Fourth Embodiment]

FIGS. 4A through 4F are section views showing a fabrication processaccording to the present embodiment. In FIGS. 4A through 4F, a logiccircuit 401 is formed on the left side of the paper and a matrix circuit402 on the right side. At first, an intrinsic (I-type) crystal siliconfilm of 600 Å in thickness is formed on a substrate (quartz) 41. Thesilicon film is then separated into islands to form island regions 42 aand 42 b for TFTs of a logic circuit and an island region 42 c for a TFTof a matrix circuit.

Further, a silicon oxide film 43 of 1000 Å in thickness is deposited onthe whole surface by means of plasma CVD (FIG. 4A).

Next, the silicon oxide film 43 is etched except a portion near achannel of the TFT of the matrix circuit. Here, the portion having awidth of 3 μm from the edge of a gate electrode to be formed later isleft. Thus, a first gate insulating layer 43 a is formed in the matrixcircuit region (FIG. 4B).

Following to that, a gate insulating film of silicon oxide is formed onthe surface of the silicon region by implementing thermal oxidation at950° C. At this time, the silicon oxide is formed to be 400 Å inthickness in the logic circuit region thermally oxidized in the state inwhich the silicon layer has been exposed. Thus, gate insulating films 44a, 44 b and 44 c are obtained (FIG. 4C).

Following to that, an aluminum film of 4000 Å in thickness is depositedby means of sputtering. It is then etched to form gate electrodes 45 a,45 b and 45 c (FIG. 4D).

Next, impurities (phosphorus and boron) are implanted to the siliconregion by using the gate electrodes as a mask by means of known iondoping. At this time, two-stage doping is implemented by changingacceleration voltage similarly to the second embodiment to form anN-type low concentration impurity region 46 d in addition to a P-typehigh concentration impurity region 46 a and N-type high concentrationimpurity regions 46 b and 46 c (FIG. 4E).

After activating the impurities, a silicon oxide film 47 of 6000 Å inthickness is formed as an interlayer insulator. Contact holes are formedtherethrough and electrode/wires 48 a and 48 b for the logic circuit andan electrode/wire 48 c for the matrix circuit are formed by aluminum.

Through the above-mentioned steps, a semiconductor integrated circuithaving a P-channel type TFT 49 a and an N-channel type TFT 49 b of thelogic circuit and a TFT 49 c of the matrix circuit is completed (FIG.4F).

[Fifth Embodiment]

FIGS. 5A through 5F are section views showing a fabrication processaccording to the present embodiment. In FIGS. 5A through 5F, a logiccircuit 501 is formed on the left side of the paper and a matrix circuit502 on the right side. At first, an intrinsic (I-type) crystallinesilicon film of 600 Å in thickness is formed on a substrate (quartz) 51.The silicon film is then separated into islands to form island regions52 a and 52 b for TFTs of a logic circuit and an island region 52 c fora TFT of a matrix circuit.

Further, silicon oxide films 53 a, 53 b and 53 c of 500 Å in thicknessare formed by means of thermal oxidation (FIG. 5A).

Next, the silicon oxide films 53 a and 53 b existing on the part of thelogic circuit are etched (FIG. 5B).

The state shown in FIG. 5B obtained by the steps so far can be obtainedalso by forming a resist film 93 except the part of the logic circuitafter separating the silicon film into the islands (FIG. 9A), byimplementing the thermal oxidation (FIG. 9B) and then by removing theresist film (FIG. 9C).

Following to that, a gate insulating film of silicon oxide is formed onthe surface of the silicon region by implementing another thermaloxidation at 950° C. At this time, the silicon oxide is formed to be 400Å in thickness in the logic circuit region thermally oxidized in thestate in which the silicon layer has been exposed. Thus, gate insulatingfilms 54 a, 54 b and 54 c are obtained (FIG. 5C).

Following to that, an aluminum film of 4000 Å in thickness is depositedby means of sputtering. It is then etched to form gate electrodes 55 a,55 b and 55 c. Further, the gate insulating films 54 a, 54 b and 54 care etched by using the gate electrodes as a mask (FIG. 5D).

Next, impurities (phosphorus and boron) are implanted to the siliconregion by using the gate electrodes as a mask by means of known iondoping. Then, a P-type impurity region 56 a and N-type impurity regions56 b and 56 c are formed (FIG. 5E).

After activating the impurities, a silicon oxide film 57 of 6000 Å inthickness is formed as an interlayer insulator. Contact holes are formedtherethrough and electrode/wires 58 a and 58 b for the logic circuit andan electrode/wire 58 c for the matrix circuit are formed by aluminum.

Through the above-mentioned steps, a semiconductor integrated circuithaving a P-channel type TFT 59 a and an N-channel type TFT 59 b of thelogic circuit and a TFT 59 c of the matrix circuit is completed (FIG.5F).

[Sixth Embodiment]

FIGS. 6A through 6F are section views showing a fabrication processaccording to the present embodiment. In FIGS. 6A through 6F, a logiccircuit 601 is formed on the left side of the paper and a matrix circuit602 on the right side. At first, an intrinsic (I-type) crystallinesilicon film of 600 Å in thickness is formed on a substrate (quartz) 61.The silicon film is then separated into islands to form island regions62 a and 62 b for TFTs of a logic circuit and an island region 62 c fora TFT of a matrix circuit.

Further, silicon oxide films 63 a, 63 b and 63 c of 500 Å in thicknessare formed by means of thermal oxidation (FIG. 6A).

Next, the silicon oxide films 63 a and 63 b existing on the part of thelogic circuit are etched. The silicon oxide film 63 c at the matrixcircuit is left (FIG. 6B).

Next, the silicon oxide films 63 a, 63 b and 63 c are etched except thesilicon oxide film 63 d at the part near the channel of the TFT of thematrix circuit. The silicon oxide film 63 d is left up to the parthaving a width of 3 μm from the edge of a gate electrode to be formedlater (FIG. 6B).

The state shown in FIG. 6B obtained by the steps so far can be obtainedalso by forming a resist film 103 except the part having the width of 3μm from the edge of the gate electrode to be formed later afterseparating the silicon film into the islands (FIG. 10A), by implementingthe thermal oxidation (FIG. 10B) and then by removing the resist film(FIG. 10C).

Following to that, a gate insulating film of silicon oxide is formed onthe surface of the silicon region by implementing another thermaloxidation at 950° C. At this time, the silicon oxide is formed to be 400Å in thickness in the part where the silicon layer is exposed. Thus,gate insulating films 64 a, 64 b and 64 c are obtained (FIG. 6C).

Next, an aluminum film of 4000 Å in thickness is deposited by means ofsputtering. It is then etched to form gate electrodes 65 a, 65 b and 65c (FIG. 6D).

Next, impurities (phosphorus and boron) are implanted to the siliconregion by using the gate electrodes as a mask by means of known iondoping. At this time, the two-stage doping is carried out by changingacceleration voltage similarly to the second or fourth embodiment toform an N-type low concentration impurity region 66 d in addition to aP-type high concentration impurity region 66 a and N-type highconcentration impurity regions 66 b and 66 c (FIG. 6E).

After activating the impurities, a silicon oxide film 67 of 6000 Å inthickness is formed as an interlayer insulator. Contact holes are formedtherethrough and electrode/wires 68 a and 68 b for the logic circuit andan electrode/wire 68 c for the matrix circuit are formed by aluminum.

Through the above-mentioned steps, a semiconductor integrated circuithaving a P-channel type TFT 69 a and an. N-channel type TFT 69 b of thelogic circuit and a TFT 69 c of the matrix circuit is completed (FIG.6F).

[Seventh Embodiment]

While the case of thickening the gate insulating film of the matrixcircuit has been shown in the third embodiment, a gate insulating filmof circuits in which priority is given to high operating speed such as ashift register circuit, a CPU circuit, a decoder circuit, a memorycircuit and others among peripheral circuits is thinned as compared to agate insulating film of circuits in which priority is given to highwithstand voltage such as a high withstand voltage switching circuit anda buffer circuit in the present embodiment.

The gate insulating film of the circuit in which priority is given tohigh operating speed among the peripheral circuits is thinned by usingthe same process with that in the third embodiment.

[Eighth Embodiment]

While the case of thinning the gate insulating film of the circuit inwhich priority is given to high operating speed has been shown in theseventh embodiment, a length of the channel is shortened further byreducing a width of a gate electrode of the circuit having the thin gateinsulating film in the present embodiment.

The present embodiment shares the same process with the third embodimentup to the step of depositing the aluminum film of 4000 to 6000 Å, or5000 Å in thickness for example, by means of sputtering after formingthe silicon oxide film.

In the present embodiment, with respect to the peripheral circuits 700,a width of gate electrodes 76 a and 76 b of the circuit 701 in whichpriority is given to high operating speed, for example, a shift registercircuit, is reduced to 1 μm which is narrower than a width of a gateelectrode 76 c (width: 2 μm) of the circuit 702 in which priority isgiven to high withstand voltage, for example, a buffer circuit, in anetching step thereafter (FIG. 7A).

Here, although the ratio of the width of the gate electrode of thecircuit in which priority is given to high operating speed to the widthof the gate electrode of the circuit in which priority is given to highwithstand voltage has been 0.5 in the present embodiment, it is notlimited to the value of the present embodiment so long as it is within arange of 0.1 to 0.5.

Next, impurities (phosphorus and boron) are implanted to the siliconregion by using the gate electrodes as a mask by means of known iondoping to form a P-type impurity region 77 a and N-type impurity regions77 b and 77 c (FIG. 7B).

Through this step, the length of the channel of the circuit in whichpriority is given to high operating speed is reduced to 80% or less ofthe length of the channel of the circuit in which priority is given tohigh withstand voltage.

Further, a length of the channel formed in contact with the gateelectrode formed in this step has almost the same length with the widthof the gate electrode.

Accordingly, the ratio of the length of the channel of the circuit inwhich priority is given to high operating speed to that of the circuitin which priority is given to high withstand voltage becomes 0.5similarly to the ratio of the width of the gate electrodes in thepresent embodiment. The ratio of the length of the channels is not alsolimited to the value of the present embodiment so long as it is withinthe range of 0.1 to 0.5, similarly to the width of the gate electrodes.

After activating the impurities, a silicon oxide film 78 of 4000 Å inthickness is formed as an interlayer insulator. Contact holes are formedtherethrough and electrode/wires 79 a and 79 b for the circuit in whichpriority is given to high operating speed and an electrode/wire 79 c forthe circuit in which priority is given to high withstand voltage areformed by aluminum.

Through the above-mentioned steps, a semiconductor integrated circuithaving a P-channel type TFT 80 a and an N-channel type TFT 80 b of thecircuit in which priority is given to high operating speed and a TFT 80c of the circuit in which priority is given to high withstand voltage iscompleted (FIG. 7C).

The pixel electrode may be added in the manner as described in thesecond embodiment.

[Ninth Embodiment]

While the case of laminating the first and second gate insulating filmsin the matrix circuit has been shown in the first embodiment, a lengthof the channel is shortened by reducing the width of the gate electrodeof the circuit in which only the first gate insulating film is used inthe present embodiment.

The present embodiment shares the same process with the first embodimentup to the step of depositing the silicon film (containing 0.1 to 2% ofphosphorus) of 3000 to 8000 Å, or 6000 Å in thickness for example, onthe gate insulating film by means of the low pressure CVD.

In the present embodiment, with respect to the peripheral circuits 800,a width of gate electrodes 86 a and 86 b of the circuit 801 in whichpriority is given to high operating speed, for example, a shift registercircuit, is reduced to 1 μm which is narrower than a width of a gateelectrode 86 c (width: 2 μm) of the circuit 802 in which priority isgiven to high withstand voltage, for example, a buffer circuit, in anetching step thereafter (FIG. 8A).

Here, although the ratio of the width of the gate electrode of thecircuit in which priority is given to high operating speed to the widthof the gate electrode of the circuit in which priority is given to highwithstand voltage has been 0.5 in the present embodiment, it is notlimited to the value of the present embodiment so long as it is within arange of 0.1 to 0.5.

The first gate insulating layer and the second gate insulating layer areetched by using respective gate electrodes as a mask to expose thesurface of the island semiconductor regions (FIG. 8A).

Next, impurities (phosphorus and boron) are implanted to the siliconregion by using the gate electrodes as a mask by means of known iondoping. Phosphine (PH₃) and diborane (B₂H₆) are used as the doping gasand the dosage thereof is 1×10¹⁵ to 8×10¹⁵ cm⁻², e.g. 2×10¹⁵ cm⁻² ofphosphorus and 5×10¹⁵ cm⁻² of boron. As a result, a P-type impurityregion 87 a and N-type impurity regions 87 b and 87 c are formed (FIG.8B).

After activating the impurities, a silicon oxide film 88 of 4000 Å inthickness is formed as an interlayer insulator. Contact holes are formedtherethrough and electrode/wires 89 a and 89 b for the circuit in whichpriority is given to high operating speed and an electrode/wire 89 c forthe circuit in which priority is given to high withstand voltage areformed by aluminum.

Through the above-mentioned steps, the semiconductor integrated circuithaving a P-channel type TFT 90 a and an N-channel type TFT 90 b of thecircuit in which priority is given to high operating speed and a TFT 90c of the circuit in which priority is given to high withstand voltage iscompleted (FIG. 8C).

Further, a length of the channel formed in contact with the gateelectrode formed in this step has substantially the same width with thatof the gate electrode. Accordingly, the ratio of the length of thechannel of the circuit in which priority is given to high operatingspeed to that of the circuit in which priority is given to highwithstand voltage is not also limited to the value of the presentembodiment so long as it is within the range of 0.1 to 0.5, similarly tothe width of the gate electrode of the present invention.

The pixel electrode may be added in the manner as described in thesecond embodiment.

[Tenth Embodiment]

A liquid crystal display fabricated by utilizing the presentspecification is called as a flat panel type display device. As suchdisplay device, there have been known ones using EL(electroluminescence) materials and using EC (electrochromic) materials,beside one utilizing the optical characteristics of liquid crystal. Theinvention disclosed in the present specification may be utilized in anactive matrix type flat panel display which uses those materials and inwhich peripheral driving circuits and the like are integrated. Theliquid crystal display (LCD) device manufactured using the presentinvention can be applied to either a transmission type or a reflectiontype.

Such display may be utilized in the following uses. FIG. 12A shows anequipment called a digital still camera, an electronic camera or a videomovie which can display motion pictures.

This equipment has functions of electronically keeping images taken by aCCD camera (or other adequate photographic means) disposed at a camerasection 2002 and of displaying the images on a display device 2003disposed within a main body 2001. The equipment may be manipulated bycontrol buttons 2004.

The invention disclosed in the present specification may be utilized inthe display device constructed as described above. Because powerconsumption may be saved by utilizing the invention disclosed in thepresent specification, it is useful for the portable equipment as shownin FIG. 12A which is supposed to be driven by a battery.

FIG. 12B shows a portable personal computer. This equipment is providedwith a display device 2104 on an openable cover 2102 attached to a mainbody 2101 and allows to input various information from a key board 2103and to run various operations.

It is also useful to utilize the invention disclosed in the presentspecification for the display device 2104 arranged as shown in FIG. 12B.

FIG. 12C shows a case when the flat panel display is utilized in a carnavigation system. The car navigation system comprises an antennasection 2304 and a main body provided with a display 2302.

Switching of various information required in navigation is can be madeby control buttons 2303. It is generally controlled by a remote controlunit not shown.

FIG. 12D shows a case of a projection type liquid crystal display. Inthe figure, light emitted from a light source 2402 is opticallymodulated by a liquid crystal display device 2403 and is turned into animage. The image is reflected by mirrors 2404 and 2405 to be projectedon a screen 2406.

As shown in the above-mentioned embodiments, the present inventionallows the TFT which can operate at high speed in low voltage and theTFT which is characterized by the high withstand voltage to be formed onone and the same substrate. Applying this to the liquid crystal displayallows the reliability, the power consumption and the characteristics tobe improved as a whole.

It is noted that the features and advantages of the present inventionmay be clearly understood if one notices on that the conventionalsemiconductor integrated circuit technology has not required to changethe thickness of the gate insulating film actively like the presentinvention. In the conventional semiconductor integrated circuit (indigital circuits in particular), voltage to be used has been all thesame within the circuit. For instance, the memory area and theperipheral circuit have been driven by single voltage in a DRAM.

However, a liquid crystal display requires a plurality of voltagesbecause voltage suitable for the liquid crystal material differs fromvoltage suitable for driving transistors in the liquid crystal display.Generally, the former is higher than the latter.

If there is a plurality of voltages, dimensions of a transistors suitedto that also have to be changed. The present invention has noticed onthis point. Accordingly, the idea of the present invention would not bebrought out from the technology of the conventional semiconductorintegrated circuit driven by single voltage. Thus, the present inventionis useful from the industrial point of view.

1. A camera comprising a display device, said display device comprising:a substrate having an insulating surface; a semiconductor layer over thesubstrate, said semiconductor layer including at least a channel region;a first insulating film comprising silicon oxide formed over thesemiconductor layer; a second insulating film comprising silicon nitrideformed over the first insulating film; a gate electrode located over thechannel region of the semiconductor layer with the first insulating filmand the second insulating film interposed therebetween; a thirdinsulating film comprising silicon nitride formed over the semiconductorlayer, the first and second insulating films and the gate electrode,wherein said second insulating film extends beyond edges of the gateelectrode; wherein said first insulating film extends beyond edges ofthe second insulating film, and wherein said third insulating film is indirect contact with an upper surface of an extending portion of thefirst insulating film and an upper surface of an extending portion ofthe second insulating film.
 2. A camera according to claim 1, furthercomprising a fourth insulating film formed over said third insulatingfilm, wherein said fourth insulating film comprises an organic resin. 3.A camera according to claim 1, wherein said semiconductor layer includesa pair of impurity regions, wherein said semiconductor layer includes atleast one lightly doped impurity region between the channel region andone of the pair of impurity regions.
 4. A camera according to claim 1,wherein said display comprises a driving circuit formed over saidsubstrate.
 5. A camera comprising a display device, said display devicecomprising: a substrate having an insulating surface; a semiconductorlayer over the substrate, said semiconductor layer including at least apair of impurity regions and a channel region; a first insulating filmcomprising silicon oxide formed over the semiconductor layer; a secondinsulating film comprising silicon nitride formed over the firstinsulating film; a gate electrode located over the channel region of thesemiconductor layer with the first insulating film and the secondinsulating film interposed therebetween; a third insulating filmcomprising silicon nitride formed over the semiconductor layer, thefirst and second insulating films and the gate electrode, said thirdinsulating film having at least one contact hole; at least one of sourceand drain electrodes formed over said third insulating film, whereinsaid second insulating film extends beyond edges of the gate electrode,wherein said first insulating film extends beyond edges of the secondinsulating film, and wherein said third insulating film is in directcontact with an upper surface of an extending portion of the firstinsulating film and an upper surface of an extending portion of thesecond insulating film, and wherein said one of the source and drainelectrodes is electrically connected to one of said pair of impurityregions through the contact hole, and wherein said one of the source anddrain electrodes is not in direct contact with the second insulatingfilm.
 6. A camera according to claim 5, further comprising a fourthinsulating film formed over said third insulating film, wherein saidfourth insulating film comprises an organic resin.
 7. A camera accordingto claim 5, wherein said second insulating film at least partly overlapsone lightly doped impurity region between the channel region and one ofthe pair of impurity regions.
 8. A camera according to claim 5, whereinsaid display comprises a driving circuit formed over said substrate. 9.A camera comprising a display device, said display device comprising: asubstrate having an insulating surface; a semiconductor layer over thesubstrate, said semiconductor layer including at least a channel region;a first insulating film comprising silicon oxide formed over thesemiconductor layer; a second insulating film comprising silicon nitrideformed over the first insulating film; a gate electrode located over thechannel region of the semiconductor layer with the first insulating filmand the second insulating film interposed therebetween; a thirdinsulating film comprising silicon nitride formed over the semiconductorlayer, the first and second insulating films and the gate electrode,wherein said second insulating film extends beyond edges of the gateelectrode; wherein said first insulating film extends beyond edges ofthe second insulating film, and wherein said third insulating film is indirect contact with an upper surface of an extending portion of thefirst insulating film and an upper surface of an extending portion ofthe second insulating film, and wherein said third insulating film is indirect contact with an upper surface of the gate electrode and sidesurfaces of the gate electrode.
 10. A camera according to claim 9,further comprising a fourth insulating film formed over said thirdinsulating film, wherein said fourth insulating film comprises anorganic resin.
 11. A camera according to claim 9, wherein said secondinsulating film at least partly overlaps one lightly doped impurityregion between the channel region and one of the pair of impurityregions.
 12. A camera according to claim 9, wherein said displaycomprises a driving circuit formed over said substrate.
 13. A cameracomprising a display device, said display device comprising: a substratehaving an insulating surface; a semiconductor layer over the substrate,said semiconductor layer including at least a pair of impurity regionsand at least one lightly doped impurity region between the channelregion and one of the pair of impurity regions; a first insulating filmcomprising silicon oxide formed over the semiconductor layer; a secondinsulating film comprising silicon nitride formed over the firstinsulating film; a gate electrode located over the channel region of thesemiconductor layer with the first insulating film and the secondinsulating film interposed therebetween; a third insulating filmcomprising silicon nitride formed over the semiconductor layer, thefirst and second insulating films and the gate electrode, wherein saidsecond insulating film extends beyond edges of the gate electrode;wherein said first insulating film extends beyond edges of the secondinsulating film, and wherein said third insulating film is in directcontact with an upper surface of an extending portion of the firstinsulating film and an upper surface of an extending portion of thesecond insulating film, wherein said second insulating film overlapssaid lightly doped impurity region.
 14. A camera according to claim 13,further comprising a fourth insulating film formed over said thirdinsulating film, wherein said fourth insulating film comprises anorganic resin.
 15. A camera according to claim 13, wherein said displaycomprises a driving circuit formed over said substrate.
 16. A cameracomprising a display device, said display device comprising: a substratehaving an insulating surface; a semiconductor layer over the substrate,said semiconductor layer including at least a pair of impurity regionsand a channel region; a first insulating film comprising silicon oxideformed over the semiconductor layer; a second insulating film comprisingsilicon nitride formed over the first insulating film; a gate electrodelocated over the channel region of the semiconductor layer with thefirst insulating film and the second insulating film interposedtherebetween; a third insulating film comprising silicon nitride formedover the semiconductor layer, the first and second insulating films andthe gate electrode, said third insulating film having at least onecontact hole; at least one of source and drain electrodes formed oversaid third insulating film, wherein said second insulating film extendsbeyond edges of the gate electrode, wherein said first insulating filmextends beyond edges of the second insulating film, and wherein saidthird insulating film is in direct contact with an upper surface of anextending portion of the first insulating film and an upper surface ofan extending portion of the second insulating film, and wherein said oneof the source and drain electrodes is electrically connected to one ofsaid pair of impurity regions through the contact hole, and wherein saidone of the source and drain electrodes is not in direct contact with thesecond insulating film, and wherein said third insulating film is indirect contact with an upper surface of the gate electrode and sidesurfaces of the gate electrode.
 17. A camera according to claim 16,further comprising a fourth insulating film formed over said thirdinsulating film, wherein said fourth insulating film comprises anorganic resin.
 18. A camera according to claim 16, wherein said secondinsulating film at least partly overlaps one lightly doped impurityregion between the channel region and one of the pair of impurityregions.
 19. A camera according to claim 16, wherein said displaycomprises a driving circuit formed over said substrate.
 20. A cameracomprising a display device, said display device comprising: a substratehaving an insulating surface; a semiconductor layer over the substrate,said semiconductor layer including at least a pair of impurity regionsand a channel region; a first insulating film comprising silicon oxideformed over the semiconductor layer; a second insulating film comprisingsilicon nitride formed over the first insulating film; a gate electrodelocated over the channel region of the semiconductor layer with thefirst insulating film and the second insulating film interposedtherebetween; a third insulating film comprising silicon nitride formedover the semiconductor layer, the first and second insulating films andthe gate electrode; a fourth insulating film formed over said thirdinsulating film comprises an organic resin; a pixel electrode formedover said fourth insulating film wherein said pixel electrode iselectrically connected to one of said pair of impurity regions, whereinsaid second insulating film extends beyond edges of the gate electrode;wherein said first insulating film extends beyond edges of the secondinsulating film, and wherein said third insulating film is in directcontact with an upper surface of an extending portion of the firstinsulating film and an upper surface of an extending portion of thesecond insulating film.
 21. A camera according to claim 20, wherein saiddisplay comprises a driving circuit formed over said substrate.
 22. Acamera comprising a display device, said display device comprising: asubstrate having an insulating surface; a semiconductor layer over thesubstrate, said semiconductor layer including at least a pair ofimpurity regions and a channel region; a first insulating filmcomprising silicon oxide formed over the semiconductor layer; a secondinsulating film comprising silicon nitride formed over the firstinsulating film; a gate electrode located over the channel region of thesemiconductor layer with the first insulating film and the secondinsulating film interposed therebetween; a third insulating filmcomprising silicon nitride formed over the semiconductor layer, thefirst and second insulating films and the gate electrode, said thirdinsulating film having at least one contact hole, at least one of sourceand drain electrodes formed over said third insulating film; a fourthinsulating film formed over said third insulating film comprises anorganic resin; a pixel electrode formed over said fourth insulating filmwherein said pixel electrode is electrically connected to one of saidpair of impurity regions, wherein said second insulating film extendsbeyond edges of the gate electrode; wherein said first insulating filmextends beyond edges of the second insulating film, and wherein saidthird insulating film is in direct contact with an upper surface of anextending portion of the first insulating film and an upper surface ofan extending portion of the second insulating film, and wherein said oneof the source and drain electrodes is electrically connected to one ofsaid pair of impurity regions through the contact hole, and wherein saidone of the source and drain electrodes is not in direct contact with thesecond insulating film.
 23. A camera according to claim 22, wherein saidsecond insulating film at least partly overlaps one lightly dopedimpurity region between the channel region and one of the pair ofimpurity regions.
 24. A camera according to claim 22, wherein saiddisplay comprises a driving circuit formed over said substrate.
 25. Acamera comprising a display device, said display device comprising: asubstrate having an insulating surface; a semiconductor layer over thesubstrate, said semiconductor layer including at least a pair ofimpurity regions and a channel region; a first insulating filmcomprising silicon oxide formed over the semiconductor layer; a secondinsulating film comprising silicon nitride formed over the firstinsulating film; a gate electrode located over the channel region of thesemiconductor layer with the first insulating film and the secondinsulating film interposed therebetween; a third insulating filmcomprising silicon nitride formed over the semiconductor layer, thefirst and second insulating films and the gate electrode; a fourthinsulating film formed over said third insulating film comprises anorganic resin; a pixel electrode formed over said fourth insulating filmwherein said pixel electrode is electrically connected to one of saidpair of impurity regions, wherein said second insulating film extendsbeyond edges of the gate electrode; wherein said first insulating filmextends beyond edges of the second insulating film, and wherein saidthird insulating film is in direct contact with an upper surface of anextending portion of the first insulating film and an upper surface ofan extending portion of the second insulating film, and wherein saidthird insulating film is in direct contact with an upper surface of thegate electrode and side surfaces of the gate electrode.
 26. A cameraaccording to claim 25, wherein said second insulating film at leastpartly overlaps one lightly doped impurity region between the channelregion and one of the pair of impurity regions.
 27. A camera accordingto claim 25, wherein said display comprises a driving circuit formedover said substrate.
 28. A camera comprising a display device, saiddisplay device comprising: a substrate having an insulating surface; asemiconductor layer over the substrate, said semiconductor layerincluding at least a pair of impurity regions and at least one lightlydoped impurity region between the channel region and one of the pair ofimpurity regions; a first insulating film comprising silicon oxideformed over the semiconductor layer; a second insulating film comprisingsilicon nitride formed over the first insulating film; a gate electrodelocated over the channel region of the semiconductor layer with thefirst insulating film and the second insulating film interposedtherebetween; a third insulating film comprising silicon nitride formedover the semiconductor layer, the first and second insulating films andthe gate electrode; a fourth insulating film formed over said thirdinsulating film comprises an organic resin; a pixel electrode formedover said fourth insulating film wherein said pixel electrode iselectrically connected to one of said pair of impurity regions, whereinsaid second insulating film extends beyond edges of the gate electrode,wherein said first insulating film extends beyond edges of the secondinsulating film, and wherein said third insulating film is in directcontact with an upper surface of an extending portion of the firstinsulating film and an upper surface of an extending portion of thesecond insulating film, wherein said second insulating film overlapssaid lightly doped impurity region.
 29. A camera according to claim 28,wherein said display comprises a driving circuit formed over saidsubstrate.
 30. A camera comprising a display device, said display devicecomprising: a substrate having an insulating surface; a semiconductorlayer over the substrate, said semiconductor layer including at least apair of impurity regions and a channel region; a first insulating filmcomprising silicon oxide formed over the semiconductor layer; a secondinsulating film comprising silicon nitride formed over the firstinsulating film; a gate electrode located over the channel region of thesemiconductor layer with the first insulating film and the secondinsulating film interposed therebetween; a third insulating filmcomprising silicon nitride formed over the semiconductor layer, thefirst and second insulating films and the gate electrode, said thirdinsulating film having at least one contact hole; at least one of sourceand drain electrodes formed over said third insulating film; a fourthinsulating film formed over said third insulating film comprises anorganic resin; a pixel electrode formed over said fourth insulating filmwherein said pixel electrode is electrically connected to one of saidpair of impurity regions, wherein said second insulating film extendsbeyond edges of the gate electrode, wherein said first insulating filmextends beyond edges of the second insulating film, and wherein saidthird insulating film is in direct contact with an upper surface of anextending portion of the first insulating film and an upper surface ofan extending portion of the second insulating film, and wherein said oneof the source and drain electrodes is electrically connected to one ofsaid pair of impurity regions through the contact hole, and wherein saidone of the source and drain electrodes is not in direct contact with thesecond insulating film, and wherein said third insulating film is indirect contact with an upper surface of the gate electrode and sidesurfaces of the gate electrode.
 31. A camera according to claim 30,wherein said second insulating film at least partly overlaps one lightlydoped impurity region between the channel region and one of the pair ofimpurity regions.
 32. A camera according to claim 30, wherein saiddisplay comprises a driving circuit formed over said substrate.